System for locating a node containing a requested resource and for selectively verifying the presence of the resource at the node

Abstract

The present invention is an improvement in a known LOCATE process used to locate resources in a computer network. The known LOCATE process always requires that information about a target resource be verified by forwarding a LOCATE request to the node owning the target resource. The present invention improves upon this process by use of selective verification. If predetermined conditions are met, a node in the network may reply to a received LOCATE request by using information about the target resource found in its cache directory. The LOCATE request need not be propagated to the node owning the target resource except for predetermined types of sessions or where past attempts to use selective verification have not been successful.

We claim: 
     
       1. In a computer network which includes a plurality of end nodes, at least one network node server for each of said end nodes, and resources associated with said end nodes and said network nodes, each said network node server having a cache directory of information relating to the location and characteristics of at least some of the resources in the network, a method of initiating establishment of a session between a source logical unit associated with a network resource at one of said end nodes and network nodes and a target logical unit associated with a network resource at another one of said end nodes and network nodes, said method comprising the steps of: generating a LOCATE request at the source logical unit, said LOCATE request identifying a target resource at the target logical unit and including a verification flag indicating whether the location and characteristics of the target resource need be verified in a reply to the LOCATE request;   transmitting the LOCATE request to the network node server for the node containing the source logical unit; and   processing the LOCATE request at the network node server, said processing step further comprising the steps of searching the cache directory of the network node for any entry relating to the target resource,   if target resource the entry is not found in the searched directory, then initiating a search for the target resource elsewhere in the network by forwarding the search request to other nodes in the network,   if the target resource entry is found in the searched directory, then checking the verification flag in the LOCATE request to determine whether the resource location and characteristics are to be verified,   if the verification flag indicates verification is not required, returning a LOCATE reply to the node containing the source logical unit, said LOCATE reply being based on the contents of the directory entry,   if the verification flag indicates verification is required, forwarding the LOCATE request to the node identified in the directory entry as containing the target resource, receiving a LOCATE reply originating at the node identified in the directory entry, and returning the LOCATE reply to the node containing the source logical unit, said LOCATE reply being based on the verified contents of the directory entry.     
     
     
       2. The method as defined in claim 1 wherein the step of generating the LOCATE request at the source node comprises the further steps of: determining whether the session to be established possesses certain characteristics;   determining whether a previous unsuccessful attempt was made to establish a session with the target logical unit without verifying the location and characteristics of the target resource; and   setting the verification flag in the LOCATE request only if the session possesses the certain characteristics and the previous session-establishing attempt did not fail while attempting to proceed without verification.   
     
     
       3. The method as defined in claim 2 wherein the step of determining whether the session possesses certain characteristics further comprises the steps of: determining whether the session is to be initiated by a primary logical unit;   determining whether the session is of a type that can tolerate failure in a subsequent session-establishment attempt;   enabling the verification flag to be set only if both determining steps yield positive results.   
     
     
       4. In a data processing network including a plurality of nodes, each of said nodes having one or more associated resources and at least some of said nodes having cache directories containing information about one or more of the resources, a method of initiating establishment of a session between two of said nodes, said method comprising the steps of: generating a LOCATE request at a first node, said LOCATE request identifying a target resources and including a verification flag indicating whether information relating to the target resource is to be verified in a reply to the LOCATE request;   transmitting the LOCATE request to at least one predetermined node having a cache directory; and   processing the LOCATE request at the predetermined node, said processing step further comprising the steps of: searching the cache directory of the predetermined node for an entry relating to the target resource,   if the target resource entry is found, and if the verification flag indicates verification is required, forwarding the LOCATE request to the node containing the target resource, receiving a LOCATE reply indicating verification and originating at the node containing the target resource, and transmitting the LOCATE reply to the first node,   and if the verification flag indicates verification is not required, generating a LOCATE reply and transmitting said LOCATE reply to the first node,     if the target resource entry is not found, initiating a search for the target resource by directing search inquiries to other nodes in the network.     
     
     
       5. The method as defined in claim 4 wherein the predetermined node is either a network node serving the first node or a network node serving the node containing the target resource. 
     
     
       6. The method as defined in claim 4 wherein the predetermined node is any node in the network. 
     
     
       7. The method as defined in claims 5 or 6 wherein the step of generating the LOCATE request at the first node comprises the further steps of: determining whether the session to be established possesses certain characteristics;   determining whether a previous unsuccessful attempt was made to establish a session with the second node without verifying the location and characteristics of the target resource; and   setting the verification flag in the LOCATE request only if the session possesses the certain characteristics and the previous session-establishing attempt did not fail while attempting to proceed without verification.   
     
     
       8. The method as defined in claim 7 wherein the step of determining whether the session possesses certain characteristics further comprises the steps of: determining whether the session is to be initiated by a primary logical unit;   determining whether the session is of a type that can tolerate failure in a subsequent session-establishment attempt;   and enabling the verification flag to be set only if both determining steps yield a positive result.   
     
     
       9. In a data processing network including a plurality of nodes, each of said nodes having one or more associated resources and at least some of said nodes having cache directories containing information about one or more of the resources, a system for initiating establishment of a session between two of said nodes, said system comprising: means for generating a LOCATE request at a first node, said LOCATE request identifying a target resource and including a verification flag indicating whether information relating to the target resource is to be verified in a reply to the LOCATE request;   means for transmitting the LOCATE request to a predetermined node having a cache directory; and   means for processing the LOCATE request at the predetermined node, said processing means further comprising: means for searching the cache directory of the predetermined node for an entry relating to the target resource,   means for forwarding the LOCATE request to the node containing the target resource and for receiving a LOCATE reply indicating verification and originating at the node containing the target resource if the target resource entry is found and the verification flag indicates verification is required,   means for generatig a LOCATE reply if the target resource entry is found and the verification flag indicates verification is not required, means for transmitting the LOCATE reply to the first node if the target resource entry is found, and   means for initiating a search for the target resource if no target resource entry is found by forwarding the LOCATE request to other nodes in the network.     
     
     
       10. The system as defined in claim 9 wherein the predetermined node is either a network node serving the first node or a network node serving the node containing the target resource. 
     
     
       11. The system as defined in claim 9 wherein the predetermined node is any node in the network. 
     
     
       12. The system as defined in claims 10 or 11 wherein said LOCATE request generating means further comprises: means for determining whether the session to be established possesses certain characteristics;   means for determining whether a previous attempt to establish a session with the second node was unsuccessful, during which attempt the location and characteristics of the target resource were not verified; and   means for setting the verification flag in the LOCATE request only if the session possesses the certain characteristics and the previous session-establishing attempt did not fail while attempting to proceed without verification.   
     
     
       13. The system as defined in claim 12 wherein the session characteristic determining means further comprises: means for determining whether the session is to be initiated by a primary logical unit;   means for determining whether the session is of a type that can tolerate failure in a subsequent session-establishment attempt; and   means for enabling the verification flag to be set only if both determining steps yield a positive result.